The present invention relates to dynamometers for testing vehicles in place and in particular to an improved flywheel assembly for such dynamometers.
Vehicle or chassis dynamometers are used primarily for two purposes: as measuring devices for determining the torque and/or horsepower output of a vehicle, and as simulation devices for simulating the inertia and road load forces to which a vehicle is subjected during actual operation of the vehicle. The present invention is concerned principally with the latter application.
Chassis dynamometer systems, when used as simulators, typically comprise a pair of rollers adapted to be driven by the driving wheels of a vehicle, a flywheel assembly mechanically coupled to the rollers, and a power absorption unit (PAU) such as a DC motor, an eddy current brake, or a hydrokinetic brake, also coupled to the rollers. The flywheel assembly serves to simulate either all or part of the inertia of the vehicle, which is a function of the vehicle's weight and is the force which must be overcome for the vehicle to accelerate or decelerate. The power absorption unit serves to simulate the road load forces, which correspond to those forces which must be overcome to maintain vehicle speed and include such factors as breakaway torque, rolling friction, and windage. In addition, when a DC motor is used as the power absorption unit, the PAU may also electrically simulate part of the inertia of the vehicle. In chassis dynamometers utilizing the latter approach, the flywheel assembly typically comprises a single mechanical flywheel which may, for example, weigh 3,000 pounds, and the PAU is then relied upon to electrically simulate, either plus or minus, the differential between the total mechanical inertia of the dynamometer system, including the flywheel, rollers, and the mechanical inertia associated with the DC motor, and the weight of the vehicle to be tested. An example of such a dynamometer is illustrated and described in U.S. Pat. No. 4,327,578, assigned to the assignee of the present invention.
Alternatively, the inertia of the vehicle may be simulated entirely by mechanical means. This is most commonly accomplished utilizing a plurality of declutchable flywheels of varying weights. Although viewed by some, including the Environmental Protection Agency, as the preferred approach, conventional dynamometers that rely completely upon mechanical flywheel assemblies for simulating vehicle inertia possess several disadvantages. For example, in order to simulate a number of different inertia values, it is necessary to provide a variety of differently weighted flywheels and a corresponding number of clutch mechanisms to selectively engage the flywheels. In a typical system, the flywheels are journalled to a shaft driven by the rollers and the clutches are connected to the flywheels and mounted to the shaft adjacent to each of the flywheels so that selective actuation of the clutches serves to selectively couple the flywheels to the shaft for rotation therewith. The multiplicity of clutches and flywheels, all mounted to the same shaft, however, can result in a flywheel assembly of substantial size and cost. In addition, because the surface area at the point of engagement between the clutch mechanisms and the drive shaft is relatively small, the torque loads applied to the clutches are substantial. Accordingly, expensive, high-load rated clutch mechanisms are required to prevent slippage. In fact, with many of the present commercial dynamometer systems, it is possible to "rock" an engaged flywheel back and forth while at rest, thus indicating the presence of "play" in the coupling between the flywheel and the shaft. Such a condition can, of course, affect the accuracy of the dynamometer.
It is the primary object of the present invention to provide an improved mechanical flywheel assembly for chassis dynamometers that obviates many of the disadvantages associated with conventional mechanical flywheel assemblies. In particular, the flywheel assembly according to the present invention comprises a plurality of flywheels of differing weights that are journalled to a stationary shaft. The flywheels are located within a cylindrically-shaped drum that is directly coupled to the drive shaft from the rollers so that the drum rotates at the speed of the rollers. Fixedly attached to the outer circumference of each of the flywheels is an inflatable clutch mechanism which, when pressurized, engages the inner wall of the drum so that its associated flywheel is forced to rotate with the drum. Because the inflatable clutch mechanism of the present invention engages the drum around the entire outer periphery of the flywheel, the mechanical coupling between the flywheel and the drum is extremely strong. In addition, due to the mechanical advantage realized by the placement of the clutch around the circumference of the flywheel instead of at the drive shaft, the torque loading on the clutch assembly is significantly reduced as well. Moreover, because the conventional shaft-mounted clutch mechanisms are eliminated, the multiple flywheels can be positioned relatively close together on the stationary shaft, thereby significantly reducing the overall length of the flywheel assembly.
Additional objects and advantages of the present invention will become apparent from a reading of the following Detailed Description of the Preferred Embodiment which makes reference to the accompanying drawings in which: